After treatment with 1 unit of lysostaphin per ml for 3 min, two strains of Staphylococcus aureus, 233 and PS 44A HJD, were transfected with phenol-extracted deoxyribonucleic acid (DNA) from the staphylococcal bacteriophages, 53 and 44A HJD, respectively. The number of transfected cells was low in both systems, approximately two in 107 enzyme-treated cells. There was a saturation effect at high concentrations of DNA; optimal results were obtained at concentrations between 10 to 25 ,ug/ml. Growth curves and fluctuation tests indicated that cells of strain 44A

SUMMARYA persistent infection of the human MCF-7 cell line (MCF-7RV) was established with the DBS strain of rubella virus at a low multiplicity of infection. Fluorescent antibody staining revealed that 100 % of the cells were positive for rubella antigens. The infected cells were refractory to superinfection with vesicular stomatitis virus (VSV) but were susceptible to herpes simplex virus type 2 (HSV-2). No interferon could be detected in infected cell culture fluid, and continuous passage in the presence of antibody did not lead to a decrease in the percentage of infected cells. Virus production in the persistently infected cells represented a 5-to 10-fold increase over primary infection. Plaque assays at 30 and 39 °C of the virus produced at 37 °C revealed the presence of temperature-sensitive (ts) mutants. If MCF-7RV cells were maintained at 30 °C, significant increases in virus production were observed, leading to cytopathic effect and destruction of the monolayer. If maintained at 39 °C, MCF-7RV cells produced less virus and demonstrated normal morphology.These data suggest that the naturally selected population of ts mutants being produced by these cells represents the mechanism by which persistence is maintained.

Pseudomonas aeruginosa, an opportunistic pathogen that often initiates infec

No abstract

A variant of Staphylococcus aureus 44A HJD was isolated by serial growth in Trypticase soy broth to which 2 M serine had been added (wt/vol). Amino acid analysis of hydrolysates of' purif'ied mucopeptides from the variant showed that they contained 1.266 serine and 2.156 glycine residues per glutamic acid residue, compared with 0.174 serine and 3.144 glycine residues per glutamic acid residue in the mucopeptide of' the parent strain. In addition to this alteration in the chemical composition of the mucopeptide, the variant lost many of the biochemical and cultural characteristics of' the parent organism. The variant was not sensitive to the lytic action of lysostaphin and was non-phage-typable. Moreover, in vitro tests indicated that the organism was coagulase negative, did not produce gelatinase or deoxyribonuclease, and did not hemolyze sheep erythrocytes. Apparently due to the change in the serine content in the cell wall of' the parent S. aureus strain, the organism had become "epidermidis-like" in its properties.